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Hi,

I am trying to prove that if

I already know that if

Thanks!

Chen

I am trying to prove that if

**o(a)**and**o(b)**are relatively prime, and**ab = ba**, then**o(ab) = o(a)o(b)**. I'd appreciate it if someone could give me a nudge in the right direction because I've spent almost 2 days on this now and I got nowhere. Which is rather annoying considering this is the first exercice in the chapter and the rest I did without a problem, so there must be something simple here that I'm missing.I already know that if

**(m, n) = 1**and**m|k**and**n|k**then**mn|k**. I think I can use this to prove what I need, if I can only show that**o(a)|o(ab)**and**o(b)|o(ab)**. (Because I've already shown that**o(ab)|o(a)o(b)**, so proving**o(a)o(b)|o(ab)**will be enough.)Thanks!

Chen

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